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Quick Overview of Filesystem Concepts

• Packages: Packages are the lowest level of ROS software organization. They can contain anything: libraries, tools, executables, etc.

• Manifest: A manifest is a description of a package. Its most important role is to define dependencies between packages.

• Stacks: Stacks are collections of packages that form a higher-level library.

• Stack Manifest: These are just like normal manifests, but for stacks.

When you look at the filesystem, it's easy to tell packages and stacks apart:

• A package is a directory with a manifest.xml file.
• A stack is a directory with a stack.xml file.

Filesystem Tools

For ROS there is lots of code spread across many packages and stacks. Navigating with command-line tools such as ls and cd would be very tedious. This is why ROS provides its own tools to help you.

Using rospack and rosstack

rospack and rosstack are part of the rospack suite. These allow you to get information about packages and stacks. In this tutorial, we are only going to cover the find option, which returns the path to package or stack.

Usage:

$ rospack find [package_name]
$ rosstack find [stack_name]

Example:

$ rospack find roscpp

Would return:

• YOUR_INSTALL_PATH/ros/core/roscpp

Using roscd

roscd is part of the rosbash suite. It allows you to change directory (cd) directly to a package or a stack.

Usage:

$ roscd [locationname[/subdir]]

Run this example:

$ roscd roscpp

To verify that we have changed to the roscpp package directory. Now let's print the working directory using the Unix command pwd:

$ pwd 

You should see:

• YOUR_INSTALL_PATH/ros/core/roscpp

You can see that YOUR_INSTALL_PATH/ros/core/roscpp is the same path that rospack find gave in the previous example.

Subdirectories

roscd can also move to a subdirectory of a package or stack.

Try:

$ roscd roscpp/include
$ pwd

You should see:

• YOUR_INSTALL_PATH/ros/core/roscpp/include

Special cases for roscd

There are a few special places you can tell roscd to go, that are not a package or stack.

roscd with no arguments

roscd without an argument will take you to $ROS_ROOT. Try:

$ roscd 
$ pwd

You should see:

•  YOUR_INSTALL_PATH/ros

This path is the same as defined by $ROS_ROOT. Try:

$ echo $ROS_ROOT

You should see:

• YOUR_INSTALL_PATH/ros

roscd log

roscd log will take you to the folder where ROS stores its log files. You might not have any use for log files yet.

Try:

$ roscd log

Using rosls

rosls is part of the rosbash suite. It allows you to ls directly in a package, stack, or common location by name rather than by package path.

Usage:

$ rosls [locationname[/subdir]]

Example:

$ rosls roscpp_tutorials

Would return:

•   add_two_ints_client         listener_unreliable
    add_two_ints_server         listener_with_tracked_object
    add_two_ints_server_class   listener_with_userdata
    anonymous_listener          Makefile
    babbler                     manifest.xml
    CMakeLists.txt              node_handle_namespaces
    custom_callback_processing  notify_connect
    listener                    srv
    listener_async_spin         talker
    listener_multiple           time_api
    listener_single_message     timers
    listener_threaded_spin

Tab Completion

It can get tedious to type out an entire package name. In the previous example, roscpp_tutorials is a fairly long name. Luckily, some ROS tools support TAB completion.

Start by typing:

$ roscd roscpp_<<< now push the TAB key >>>

After pushing the TAB key, the command line should fill out the rest.

• $ roscd roscpp_tutorials/

This works because roscpp_tutorials is currently the only ROS package that starts with roscpp_.

Now try typing:

$ roscd tur<<< now push the TAB key >>>

After pushing the TAB key, the command line should fill out as much as possible:

• $ roscd turtle

However, in this case there are multiple packages that begin with turtle.

Try typing TAB another time. This should display all the ROS packages that begin with turtle

•   turtle_actionlib/  turtlesim/         turtle_teleop/     turtle_tf/

On the command line you should still have

• $ roscd turtle

Now type a s after turtle and then push TAB

$ roscd turtles<<< now push the TAB key >>>

Since there is only one package that start with turtles, you should see:

• $ roscd turtlesim/

Review

You may have noticed a pattern with the naming of the ROS tools:

• rospack = ros + pack(age)
• rosstack = ros + stack
• roscd = ros + cd
• rosls = ros + ls

This naming pattern holds for many of the ROS tools.

Now that you can get around in ROS, let's create a new package.